1. Field of the Invention
The present invention relates to a silver halide photographic light-sensitive material, and more particularly to a silver halide photographic light-sensitive material which not only has high gradation and high sensitivity, but also has low fog and excels in storage stability.
2. Description of the Related Art
In recent years, a demand for silver halide photographic light-sensitive materials has been increasily strict. In particular, it has been increasingly requested that the material have high sensitivity and provide higher-quality images. This demand compels the researchers concerned to work harder in their effort to provide better silver halide photographic light-sensitive materials.
Silver halide emulsions for use in silver halide photographic light-sensitive materials are subjected to various types of chemical sensitization. Typical examples of chemical sensitization are: chalcogen sensitization (e.g., sulfur sensitization, selenium sensitization, or tellurium sensitization), precious-metal sensitization (e.g., gold sensitization or platinum sensitization), reduction sensitization, and a combination of these sensitizations.
As a sensitization, tellurium sensitization and tellurium sensitizers are generally described in several references, such as U.S. Pat. Nos. 1,623,499, 3,320,069, 3,772,031, 3,531,289, and 3,655,394, British Patents 235,211, 1,121,496, 1,295,462, and 1,396,696, and Canadian Patent 800,958. However, specific tellurium sensitizers are described in detail in a few references only, such as British Patents 1,295,462 and 1,396,696, and Canadian Patent 800,958.
As is described in, for example, Canadian Patent 800,958, a tellurium sensitizer, when applied singly to a silver halide emulsion, the emulsion will be more sensitive, less fogged, and better in contrast than if it is sensitized by a sulfur sensitizer commonly used in the art. When a telluruim sensitizer and a precious-metal sensitizer, particularly gold sensitizer, are applied, thus achieving gold-tellurium sensitization on a silver halide emulsion, the emulsion will have higher sensitivity than if it is subjected to sulfur-gold sensitization, but will be more fogged and will have its gamma value reduced, inevitably causing low gradation. Hence, it has ben strongly demanded that measures be taken to solve the problems with the tellurium sensitizer.
Even if the emulsion has been tellurium-sensitized only, it does not serve to improve the storage stability (i.e., the stability in sensitivity in a high-temperature, high-humidity condition) of the light-sensitive material using the emulsion. In view of this, too, some improvement should be made in tellurium sensitization.
Because of the above-mentioned problems with the tellurium sensitization, silver halide emulsions are usually subjected to two or more chalcogen sensitizations, for example a combination of sulfur sensitization and selenium sensitization. In practice, tellurium sensitization has not be employed. As a matter of fact, only a few references disclose tellurium sensitization. Most of the patents specified above describe the sulfur sensitization and the selenium sensitization which were experimentally carried out.
On the other hand, recently it has been found advisable to use monodispersed silver halide emulsions. A number of inventions concerning the use of monodispersed silver halide emulsions have been disclosed to the public. For example, JP-A-59-180536, JP-A-59-185329, JP-A-59-185330, JP-A-59-181337, JP-A-59-187338, JP-A-61-67845, and JP-A62-196645 disclose selenium sensitization of a monodispersed silver halide emulsion. ("JP-A" means Published Unexamined Japanese Patent Application.) However, these references make no mention of a combination of selenium sensitization and tellurium sensitization, which may solve the problems with tellurium sensitization.
Of the references specified above, JP-A-61-67845 teaches that it is useful to chemically ripen monodispersed core/shell-type silver halide grains in the presence of at least one water-soluble salt selected from the group consisting of Rh, Pd, It, and Pt, a chalcogen sensitizer, and a gold sensitizer. Tellurium sensitization is one of various chalcogen sensitizations. However, JP-A-61-67845 clarifies that a sulfur sensitizer and a selenium sensitizer are preferred as chalcogen sensitizers, and describes only a combination of sulfur sensitization and selenium sensitization. Althrough this publication refers to tellurium sensitization, it discloses no technique, whatever, of tellurium-sensitizing a monodispersed silver halide emulsion. It is impossible to expect, from the technical disclosure of the publication, any specific advantages resulting from tellurium-sensitizing a monodispersed silver halide emulsion.